The present invention is directed generally to cardiac pacers, and more particularly to an input/output circuit for a cardiac pacer programmable for use with either bipolar or unipolar leads.
Implantable battery operated cardiac pacers require one or more pacer leads for establishing electrical connection between their input/output terminals, and the atrium and/or the ventricle of the heart. Such leads, which are typically of the endocardial type for direct implantation in the heart, may be of either unipolar (UNIP) construction, wherein the implanted lead provides a cathode electrode and an anode electrode is provided through the pacer housing or other suitable means, or of bipolar (BIP) construction, wherein the implanted lead provides both the cathode and anode electrodes, and the pacer housing is isolated from the electrical circuit.
Depending on the particular application, the use of one or the other of the two lead types may be advantageous. Unipolar leads have the advantage of being physically smaller, and of providing less energy loss and greater sensitivity than bipolar leads. Bipolar leads have the advantage of providing improved noise rejection, improved immunity against undesired muscle stimulation, and reduced susceptibility to artifacts resulting from patient movement.
The choice of lead type is made by the physician at the time of implant, depending on the particular pacing requirements of the patient and any problems encountered with either the sensing or pacing functions. Once implanted, the pacer and leads are inaccessible except by invasive surgical procedures. In the past in those instances where a change in lead configuration has been necessary (i.e. BIP to UNIP, or UNIP to BIP), it has been necessary to surgically remove the pacer for reconfiguration, thereby subjecting the patient to the risk of complications.
The problem of post-implant lead reconfiguration is more prevalent with pacers having two electrodes; one for sensing and/or pacing the atrium, and one for sensing and/or pacing the ventricle. These pacers are typically utilized in treating more complex cardiac dysfunctions and are susceptible to cross-talk between atrial and ventricular leads, as well as to the previously outlined sensitivity and isolation problems. While many of such two electrode pacers incorporate a multiplex circuit which enables the pacer to be non-invasively reprogrammed by means of external control apparatus, there has heretofore been no provision for reconfiguring the pacer input/output circuitry for alternate lead arrangements.
The present invention provides an input/output circuit for a cardiac pacer which enables the use of either UNIP or BIP lead configurations, for either sensing or pacing, as programmed by the physician, eithout the necessity of making physical changes to the pacer or its leads.
Accordingly, it is a general object of the present invention to provide a new and improved cardiac pacer.
It is a more specific object of the invention to provide a new and improved cardiac pacer having an input/output circuit programmable for use with either UNIP or BIP pacer leads.
It is a more specific object of the invention to provide an input/output circuit for a dual channel cardiac pacer which offers improved sensitivity and inter-channel isolation.